since 10 years i own a pair of IMF TLS 50 speakers.
https://www.dropbox.com/s/6576gsaiunzm8tx/IMF%20TLS%2050%20MKII.jpg
They were kept in a garage before, unused for 15 years or so. They had a very nice sound until last autumn. I had them running the hole evening, unfortunately the Amp broke down and something happened with the speakers. I got a new Amp (Yamaha RS500 with 2x75W RMS, 105W max. similar to the old one) and recognized that the sound changed. Voices sound as if the person is behind a wall. As if there are less high frequencies. Imagine you adjust the Treble as low as possible. But its worse I would say. I'm not sure how to describe in a different way, but they don’t sound as they usually do.

With the new parts they seem to sound a little better, but not as they did before. The bass is much to deep and strong. I have to adjust the bass as low as possible at the amp, then ist ok. Voices still sound strange, deep and low, but clearly to hear.
I can also hear a difference between both speakers. The one with the changed capacitor sounds better. Voices are better. But the other one ( no destroyed cap, only changed the resistor) is as bad as before. I tested several Frequencies from 3000Hz to 20.000 Hz with an interval of 1000 Hz. Every frequency was audible.

Now i’m not sure what to check next. There are no more broken parts that could be identified by eye. I need a multimeter now, i guess.
- Should i check the crossover for right voltages/Frequencies? (Wouldn’t help much, when i don’t know the correct values)
- Should i check the Tweeters? For what values should I check?

I would really like to get them running again. They are very valuable to me.
It would be very nice if you can help me out.

There are a couple of things you can do.
Falcon acoustics can sell you a complete set of capacitors. It's worth changing them all.
If that doesn't help, run some white noise (from an FM tuner) or similar and cover each drive unit in turn with a piece of card. This should help you determine if any of them is not working.
After that it may be necessary to do some swapping around of drive units between pairs to determine whether the crossover is still at fault.

In the (more) bad speaker i changed 2 x 4mfd capacitors with some new ones i still had from the first order. I guess that really changed something. Now the bad one sounds like the other Speaker. But they are still not as good as they used to be.

I ran some withe noise with Audacity from my Laptop, but i couldn't really point out if there is a tweeter not working.
But i'm pretty sure every drive is working (otherwise i couldn't hear frequencies between 1000 - 20.000 Hz ), but i dont know if they are a 100% fine.

I guess i have to change the other capacitors, too.
But the coils should be ok , right ? What would i hear when they aren't ?

Either listen to the tweeters at low to mid level with the tweeters connected using a decently large cap say 10-20µF, or at least turn the bass controll all the way down.

The sound should sound clear, if weak in bass and midrange. If it has a buzzing or "grainy" crackling quality to it the tweeter is shot. The amp that broke down probably generated a square wave or something similar with a lot of high frequency at its last moments. The blown componenets gave some protection to the tweeter but even if the wire did not burn straigt through other bad things could have happened.

The heat can have deformed the bobbin of the coil so it is no longer circular and rubs against the magnet structure.

The tweeter is a Audax behind a 18 dB/octave filter both pretty standard, if they are broken a replacement with modern dome (Peerless, Seas etc) should work fine. If you replace the tweeter try having the super tweeter both connected and disconnected and find out what you like best

I just rebuilt my TLS-50MkII's. I used the Coles 16ohm replacement from Falcon Acoustics. I also had to replace the mid's with the Monacor. They have the Audax replacements as well. So drivers other than the KEF B200 shouldn't be an issue to replace.

I would suggest doing ALL of the Caps. I replaced mine with the kit they have and man did it wakeup the IMF's! _________________Kef 107's-"One of the few full-range loudspeakers that I have experienced to touch the soul—not just of the music, but of the listener."—John Atkinson

I would strongly recommend as above to replace all resistors and capacitors with new from Falcon. Also, unsolder one leg from each inductor and measure the resistance and inductance (if possible) and compare each crossover to its mate. Its possible that there was damage to any of the parts so important to check them all. Also inspect all solder joints and PC board traces for any signs of damage or breakage.

Your pictures show that the midrange has been replaced with a Visaton midrange. I would suggest getting the Falcon recommended Monacor midrange replacement for the original IMF / ELAC midrange to restore the normal balance. Also, check each tweeter and supertweeter for at least DC resistance to note if the coils are working properly, same for the woofer._________________Regards,